Prince William and Prince Harry have had a strained relationship recently, but that doesn't mean they have forgotten their promise to their friend.

The two princes, despite their disagreement, jointly signed a letter this past December dedicated to a friend from their school days who sadly passed away in 2002 at the age of 18.

The letter was included in the order of service for the 12th annual Henry van Straubensee Christmas Carol Concert, a fundraiser for the Memorial Fund honoring the late Henry.

Both princes were friends with Henry, while Harry was a classmate at Radgrove Preparatory School; the two royals became co-sponsors of the fund in 2009 and remain close friends with Henry's brother Thomas, godfather to Princess Charlotte, and Archie's godfather Charlie Marie Claire" previously reported.

"I believe everyone here tonight would agree that what Claire and Alex [van Straubensee, Henry's parents] have accomplished since 2009 is extraordinary," the royal brothers wrote (Hello!)

." As you are all gathered under this roof tonight, the charity is supporting 51 nursery schools, elementary school and secondary schools in rural Uganda, where 1,700 projects have been completed and more than 35,000 children benefit each year by receiving an education they could not otherwise receive! They are benefiting from the support of the school."

Although William and Harry were not able to attend the service in person, it was important to them to pay their respects to Henry. Pippa and James Middleton and their wives, however, did attend, as they had in previous years.

"For those of us who knew Henners," the two royals continued, "we will always miss his mischievous charm and hilarious sense of humor.

"Henry's legacy will live on through the wonderful accomplishments his mother and father have made over the years. [As funds allow, they will continue to monitor the school, ensuring that children in southeastern Uganda receive a vital education, providing them with the opportunity to rise above poverty as they grow up, and hopefully their children will do so in the future.

"Thank you for your continued support in making this possible and for the undying support of the van family, whom we all love and adore.